Device for collecting solar energy

ABSTRACT

A device for gaining solar energy comprises a integral unit with a casing ( 10 . . . 13 ). The casing comprises reflection means ( 20 ) with a hollow reflector surface ( 25 ) and is closed off by refraction means ( 30 ) with an entry surface ( 35 ) for entering sunlight. The refraction means and reflection means are each rotatably arranged around a rotation axis ( 71, 72 ) and their orientation relative to each other is continuously adjusted to the current position of the sun in the sky using positioning means provided for that purpose. The casing comprises a number of dustproof, but nevertheless ventilating chambers. The first chamber ( 100 ) is situated between the refraction means ( 30 ) and the reflection means ( 20 ) and comprises energy-conversion means ( 40 ) at least near to the focal point of the reflector surface ( 25 ). A second chamber ( 200 ) is situated between the reflection means ( 20 ) and the base part ( 13 ) of the casing and comprises positioning means ( 51, 53 ) for rotating the refraction means ( 30 ) and the reflection means ( 20 ).

The present invention relates to a device for gaining solar energy comprising reflection means with a reflector surface, the reflector surface having at least one focal point, and comprising refraction means with an entry surface for entering sunlight and an exit surface facing the reflector surface of the reflection means, the refraction means being rotatably arranged around a first rotation axis, the reflection means being rotatably arranged around a second rotation axis, an entry area of energy conversion means being provided at least near the at least one focal point of the reflector surface, and positioning means being provided for rotating the refraction means around the first rotation axis and rotating the reflection means around the second rotation axis in dependence on the current position of the sun.

Such a device is known from European patent application EP 2005074. This device comprises refraction means in the form of a prismatic lens which captures sunlight from a first direction at an entry surface and emits it at an exit surface in a second, deviating direction. A reflector body is positioned with a concave reflector surface in this second direction in order to capture the light thus refracted by the refraction means and to concentrate it in a focal point of the reflection means. In or near to this focal point a photovoltaic cell is located which converts sunlight into electric energy. With a view to optimizing the performance of the device the lens and the reflector are both rotatably mounted around a rotation axis and provided with positioning means which continuously adjust their orientation relative to each other to the current position of the sun. Such a continuous or periodical adjustment of the direction to the ever changing position of the sun in the sky encourages an optimal fraction of sunlight to reach the photovoltaic cells. Accordingly a substantial improvement of the operational efficiency of such a device can be obtained, which benefits its economic feasibility to a large degree.

Said economic feasibility is also dependent on other factors. Firstly, this is a geographical location where the device is to be set up. In areas with more hours of sun more energy can be obtained than in areas where the sun is in the sky for a shorter period of time. Furthermore, technical factors are important, such as the durability and reliability of the device, which should preferably operate itself unmanned and in a fully autonomous way. Finally, economic factors play a role such as the availability and cost price of the surface area, especially if the device is to be used in a park of a large number of similar devices in order to achieve a larger total output.

Unsurprisingly therefore desert areas in particular are preeminently suited for using such installation for gaining solar energy. This, however, does mean that the device has to be able to withstand extreme climatological phenomena which happen to be characteristic for desert areas, such as sand drifts and large daily fluctuations in temperature. The present invention inter alia intends to provide for a device of the type described in the opening paragraph also having a reliable and long-lasting uninterrupted operation under such circumstances.

In order to accomplish the intended goal a device for obtaining energy from sunlight of the type described in the opening paragraph according to the invention is characterized in that the reflection means, the refraction means, the positioning means and the conversion means extend from a integral unit with a common casing, the refraction means being rotatable around the first rotation axis with respect to a base part of the casing and provided with primary driving means capable of and set up to impose thereupon a rotation around the first axis with respect to the base part of the casing, the reflection means being rotatably arranged round the second rotation axis within the casing and provided with secondary driving means to impose thereupon a rotation around the second axis with respect to the base part, and the refraction means and the reflection means enclosing an at least almost dustproof closed off chamber, though ventilating in terms of air and water vapour, between the exit surface of the refraction means and the reflector surface of the reflection means, the chamber at least containing said entry area of the conversion means.

Accordingly the refraction means and the reflection means are united with each other in a integral unit, which allows the space between the refraction means and the reflection means containing the conversion means to be adequately closed off. Sand and dust therefore have no or hardly any chance of penetrating, whereas water vapour is nevertheless able to escape instead of condensing when the ambient temperature falls, such as say at night. The device is thus preeminently suited for use in desert areas with large daily temperature fluctuations, but can of course also be used advantageously in less extreme places.

A particular embodiment of the device in this context is further characterized in that the casing between the base part and the reflection means comprises a second, at least almost dustproof chamber, the primary driving means and the secondary driving means being at least substantially arranged in the second chamber. Accordingly the driving means are also protected against dust and sand within a chamber of the unit adequately closed off for this purpose. Such a unification of all relevant components in a common, adequately closed unit moreover decreases the installation time and installation costs of the device which only needs to be put in place and connected to an energy consumption network.

In addition to serving as an optical component the reflection means may serve as a structural element in the device. In that context a further special embodiment of the device according to the invention is characterized in that the reflector surface extends from a reflector body which almost fully separates the first chamber and the second chamber from each other, and more in particular that the reflector body leaves an at least almost dustproof, but nevertheless ventilating slit between the first chamber and the second chamber. Thus the reflector body closes off the first chamber and the second chamber almost completely from each other in a way which, though it is dustproof, is nevertheless ventilating via for example said slit. The intentional ventilation of the chambers not only furthers moisture and water vapour management within the device but also a leveling of the temperature. The risk of undesired condensation and mechanical stress with the device can thus be restricted.

A further special embodiment of the device according to the invention is characterized in that the primary driving means comprise a primary motor unit or actuator which may or may not be directly rigidly connected to a first of the refraction means and the base part of the casing and with an output shaft which may or may not engage directly with a toothing, which extends from a second of the refraction means and the base part of the casing. Thus the base part offers a point of reference relative to which the refraction means are positioned. This or at least something similar is possible with respect to the reflection means. For this purpose a further special embodiment of the device according to the invention is characterized in that the secondary driving means comprise a secondary motor unit or actuator which may or may not be directly rigidly connected to a first of the reflection means and the base part of the casing and with an output shaft which may or may not engage directly with a toothing which extends from a second of the reflection means and the base part of the casing. For the motor unit/actuator using a step motor or stepper motor is preferred. That enables one to impose an extremely accurate angle of rotation with respect to the relevant rotation axis upon the refraction means or reflection means respectively.

Condensation in the first chamber in which the conversion means and the reflection surface are located will inevitably lead to temporary or even permanent lower efficiency of the device, in particular if the consequence is a deposition of salts or oxidation at one of the surfaces. In order to further reduce the risk of this happening a further embodiment of the device according to the invention is characterized in that the first chamber comprises reversible moisture-absorption means which are in open communication with the reflector surface and the exit surface of the refraction means, and more in particular that the absorption means comprise a porous absorption body, in particular a body containing cellulose, more in particular a body of wood. The idea behind this is that an excess of water vapour will be counteracted in the first place by an absorption of moisture in the absorption body in stead of by condensation. If, subsequently, for example by warming, a non-saturated atmosphere arises, the body will release this moisture to its surroundings. Due to this reversibility the body will not be saturated so quickly and may operate in this manner for a long time.

Aside from the reflection means the refraction means can also in addition to an optical function fulfill a structural role within the device according to the invention. For this purpose a further special embodiment of the device according to the invention is characterized in that the refraction means comprise a refraction body which at least almost fully hermetically closes off the casing on a main side. The refraction body thus forms a lid which closes off the casing. Good empirical knowledge in that respect was gained with a special embodiment of the device whereby the refraction means comprise a prismatic lens, in particular a Fresnel lens.

In order to boost efficiency and output a preferred embodiment of the device according to the invention is characterized in that the reflector surface comprises a number of segments, each with its own focal point, and that secondary refraction means are included at least near each of the focal points of the segments, having a focal point which at least almost coincides with a main surface of the conversion means. Thus the incident sunlight, after refraction by the refraction means, can be converged from the segments to their individual focal points. The secondary refraction means in turn provide for a concentration of the light on the operative main surface of the conversion means which accordingly are allocated at least almost all the light which entered at the entry surface.

A further special embodiment concerns conversion means in the shape of one or more photo-voltaic cells which thus convert the sunlight into electricity. A further special embodiment of the device is characterized in that the conversion means are rigidly connected to the reflection means. Thus the conversion means are always located in the one or more focal points of the reflection means regardless of the their orientation relative to the second rotation axis.

The invention will now be explained further based on an example of an embodiment and the accompanying drawing. The drawing shows in:

FIG. 1 a cross section of the example of an embodiment of a device according to the invention.

The FIGURE is incidentally purely schematic and not drawn completely to scale. In particular some of the dimensions may be exaggerated to a greater or lesser extent in their rendering for the sake of clarity. Corresponding parts in the FIGURE are indicated with the same reference numerals as much as possible.

Renewable energy is important to an increasing degree as an additional source of energy as fossil fuels are being depleted or becoming more difficult to recover and world energy needs are nevertheless showing an upward trend. In this regard solar energy can be an important factor, provided that a sufficiently high performance and a sufficiently high output can be achieved. The present invention provides for a device for gaining solar energy which can satisfy both these aspects. An example of such a device is shown in FIG. 1.

The device comprises an at least almost fully dustproof closed casing 10. Within are located the reflection means 20 in the form of a hollow mirror. Although the mirror 20 can be constructed with a single concave, in particular a hyperbolic reflector surface 21, with a single focal point, this example uses reflection means with a multiple hollow reflector surface with a number of separate lobes 22. In this example the reflector surface comprises four of such lobes each with an individual focal point.

The energy conversion means are situated in or near the focal points in order to obtain a form of energy from the sunlight concentrated thereon. In this example the energy conversion means comprise one or more photo-voltaic cell bodies in combination with inter alia a secondary optical system 45 consisting of a number of lenses. The lenses 45 are placed with an entry surface in or near the focal point of one or more of the lobes 22 of the mirror. The focal points of the individual lenses in turn at least almost coincide with an active surface of the photo-voltaic cell or cells 40. Incidentally with respect to the energy conversion means one can also use a helio-thermic device for obtaining heat, but in the present example one or more photo-voltaic cells which convert incident sunlight into electricity are used. Together with the photo-voltaic cells the secondary optical system 45 is fixedly connected to the mirror 20 by a set of rigid arms 47, so that the conversion means will always be situated in the focal point of the mirror. For a further example of the embodiment of the photo-voltaic conversion means used here reference is made to an also pending patent application of the applicant, the content of which should be considered as cited and inserted here.

The casing 10 moreover comprises refraction means in the form of a prismatic lens at a main entry side. The lens is formed by a plate-shaped body 60 which closes off the casing at the main entrance side. The body can be formed of glass, but from the point of view of saving costs this example uses a clear, transparent plastic, in particular polymethyl methacrylate or polycarbonate, which may or may not be provided with an additional transmission coating in order to counteract reflection on an entry surface thereof as much as possible. At an exit side the surface of the plate-shaped body 60 has been processed in that a prismatic saw tooth profile has been arranged therein. Accordingly the plate-shaped body acts as a so-called Fresnel lens, with which light, impinging at an angle, is bent towards an optical main axis. If desired, the plate-shaped body 60 can be covered with a glass plate for protection against erosion.

The lens is firmly connected to a first shell portion 11 of the casing 10, the shell portion having driving means in the form of a stepper electric motor 31 which with an output shaft and a sprocket 35 engages with a tooth wreath 36 which extends from a base part 13 of the casing. Accordingly during operation the shell portion 11 and as a result the lens 60 are rotatable around the first rotation axis 71. Due to this rotation the extending optical main axis of the lens 60 can be continuously oriented and adjusted to allow it to coincide as accurately as possible with an incoming main axis of the reflector surface 21 of the mirror 20. As a result sunlight which comes in at the main entry side of the lens 60 will be fully or almost fully concentrated in one or more focal points of the reflector surface 21 and from there, due to the secondary optics 45, converge to the common focal point in an entry area of the photo-voltaic cell(s) 40.

In order to enable this common focal point to coincide as accurately as possible with said entry area, i.e. the active surface of the photo-voltaic cell(s) 40, the reflection means 20 are rotatably arranged around a second rotation axis 72 en also provided with (secondary) driving means so as to be able to impose a rotation around that axis 72. The secondary driving means with which the reflection means can thus be oriented relative to the lens 60, comprise a second stepper electric motor 32. With a sprocket 37 an output shaft thereof engages with a second tooth wreath 38 in the base part 13 of the casing 10.

In this example the second rotation axis 72 coincides with the first rotation axis 71, however, as such this is not essential. What is significant is that accordingly the lens 60 and the mirror 20 can be adjusted independently of each other and that their orientation relative to each other can thus continuously be adjusted to the current position of the sun in the sky. As a result it is possible to capture a fraction of sunlight which is as large as possible and to concentrate it on the active surface of the conversion means 40. The device thus achieves an unparalleled performance per unit of surface area used for this purpose compared to more conventional photo-voltaic solar panels and helio-thermic solar collectors. For further clarification of the functioning of this device reference is made to said prior European patent application of the applicant published under number EP2005074 and whose content should be considered cited and inserted here.

The final effective output of the device will depend to a large degree on the hours of sun and the intensity of the sun to which the device is exposed on a daily basis. Moreover, the economic payback period of an investment relating to an installation of the device will also depend on the local land price and installation costs. In view of these and other factors it is preferable to use the device in a park of a large number of these devices and to build such parks in desert areas.

Since according to the invention, as in the example shown, the reflection means 20, the refraction means 60, the positioning means 31, 32 and the conversion means 40 all extend from a integral unit which is set in a common casing 10, installation time and hence installation costs can be kept within relative limits. Moreover, the installation accordingly does not require any special knowledge from the responsible operator.

In order to be able to withstand climatological circumstances which happen to be characteristic of desert areas, such as sand drifts and large daily fluctuations in temperature, the device comprises an at least almost dustproof, but nevertheless ventilating first chamber 100, in the casing 10 between the lens 60 and the reflection means 20. The conversion means 40 with the secondary optical system are arranged within, so that these, as well as the reflector surface 21, are well protected against the influence of dust and sand.

Due to the fact that the chamber 100 is nevertheless ventilating, condensation inside is counteracted. For this purpose the reflector body 20 maintains a slit or cleft with the encircling shell 11 at the circumference thereof. Over this slit a strip of filter material is arranged which is dustproof but nevertheless permeable by water and water vapour. For this purpose an advanced membrane filter can be used, such as of a plastic available commercially under the brandname GoreTex, or a similar material, or else a sufficiently finely meshed non-woven material made of an appropriate plastic, such as polyester. The chamber 100 can thus ventilate sufficiently and exchange water vapour with the surroundings, yet sand and dust cannot enter.

Should the air in the chamber 100 nevertheless go below the dew point during nightly cooling, as a result of which condensation could still occur, an absorption body 90 has been included in the chamber as an extra safeguard. This absorption body is capable of receiving and relinquishing water, so that saturated water vapour can be effectively expelled from the air instead of settling down on one of the optical components. As such several different porous materials lend themselves to such reversible behavior. In this example a wooden ring 90 is used for this purpose which is arranged at a top side in the chamber, outside the optical operational area of the device. Thus the body does not disturb the optical functioning and efficiency of the device, but is nevertheless in open communication with the atmosphere in the chamber and capable of regulating its moisture content.

The reflection body 20 separates the first chamber 100 from a second chamber 200, which is also at least almost dustproof and ventilating. This second chamber 200 has room for the primary driving means 31 and the secondary driving means 32. A second shell portion 12 of the casing forms an outer limit of the second chamber 200. A seal, not shown in further detail, between the first shell portion 11 and the second shell portion 12 allows for a rotation of the lens 20 within the casing but nevertheless keeps the second chamber dustproof to a sufficient degree. As a result the driving motors 31, 32 in the device and the transmission parts 35 . . . 38 associated with them are also well protected against external (weather)influences and in particular the influence of sand and dust.

The second chamber 200 is separated by a ground plate 250 from a third chamber 300, which is further delimited by the base part 13 of the casing. With a second shell portion 12 the casing rests on the base part 13 and both are stationary during operation. Accordingly the device is arranged completely in an integral and is therefore relatively easy and fast to install on site.

Various materials can be used for the shell portions 11, 12 and the base part. In this example a impact-resistant plastic is used. More specifically the base part is made of polypropylene and for the shell portions Acrylonitrile Styrene Acrylate (ASA) is used. The different parts are, where possible, produced by injection moulding. Precision parts such as for example the prismatic surface of the lens and the reflector surface of the mirror can potentially be treated in order to remain to a sufficient degree within the relatively narrow applicable dimension tolerance. The reflector body 20 can also be mainly made of plastic, the body at the reflector surfacing being provided with a reflecting coating.

For the purpose of connecting to a local distribution network the device has electronic conversion means adequately adapting a power discharge of the photo-voltaic cell(s to a type and size of that network. To enable a simple replacement in case of malfunctioning or maintenance these electronics are arranged on a plug-in card and arranged in one of the chambers of the device. At an exit of the device the power thus released can be directly connected to the network.

Although the invention was described above solely using one single example it should be clear that the invention is certainly not limited to this. On the contrary, in the context of the invention many variations and embodiments are available to the average person skilled in the art. 

1. Device for gaining solar energy comprising reflection means with a reflector surface having at least one focal point, and comprising refraction means with an entry surface for entering sunlight and an exit surface facing the reflector surface of the reflection means, the refraction means being rotatably arranged around a first rotation axis, the reflection means being rotatably arranged around a second rotation axis, an entry area of said energy conversion means being provided at least near the at least one focal point of the reflector surface, and positioning means being provided for rotating the refraction means around the first rotation axis and for rotating the reflection means around the second rotation axis in dependence on a current position of the sun, characterized in that the reflection means, the refraction means, the positioning means and the conversion means extend from a integral unit with a common casing, the refraction means being rotatable around the first rotation axis with respect to a base part of the casing and provided with primary driving means capable of and set up to impose thereupon a rotation around the first axis with respect to the base part, the reflection means being arranged rotatably round the second rotation axis within the casing and provided with secondary driving means in order to impose thereupon a rotation around the second axis with respect to the base part, and in that the refraction means and the reflection means enclose an at least almost dustproof, though ventilating in terms of air and water vapour, closed off chamber between the exit surface of the refraction means and the reflector surface of the reflection means, the chamber comprising at least said entry area of said conversion means.
 2. Device according to claim 1 characterized in that the casing comprises a second, at least almost dustproof chamber, between the base part and the reflection means, and the primary driving means and the secondary driving means are arranged at least substantially in the second chamber.
 3. Device according to claim 2 characterized in that the reflector surface extends from a reflector body which almost completely separates the first chamber and the second chamber from each other.
 4. Device according to claim 3 characterized in that the reflector body leaves an at least almost dustproof, but nevertheless ventilating slit between the first chamber and the second chamber.
 5. Device according to claim 1 characterized in that the primary driving means comprise a primary motor unit or actuator which may or may not be directly rigidly connected to a first of the refraction means and the base part of the casing and with an output shaft which may or may not engage directly with a toothing, which extends from a second of the refraction means and the base part of the casing.
 6. Device according to claim 1 characterized in that the secondary driving means comprise a secondary motor unit or actuator which may or may not be directly rigidly connected to a first of the reflection means and the base part of the casing and with an output shaft which may or may not engage directly with a toothing which extends from a second of the reflection means and the base part of the casing.
 7. Device according to claim 1 characterized in that the first chamber comprises reversible moisture-absorption means which are in open communication with the reflector surface and the exit surface of the refraction means.
 8. Device according to claim 7 characterized in that the absorption means comprise a porous absorption body, in particular a body containing cellulose, more in particular a body of wood.
 9. Device according to claim 1 characterized in that the refraction means comprise a prismatic lens, in particular a Fresnel lens.
 10. Device according to claim 1 characterized in that the refraction means comprise a refraction body which at least almost fully hermetically closes off the casing on a main side.
 11. Device according to claim 1 characterized in that the reflector surface comprises a number of segments, each with its own focal point, and that secondary refraction means are included at least near each of the focal points of the segments, having a focal point which at least almost coincides with a main surface of the conversion means.
 12. Device according to claim 11 characterized in that the conversion means comprise at least one device from a group comprising a photovoltaic cell and a heliothermic element.
 13. Device according to claim 1 characterized in that the conversion means are rigidly connected to the reflection means. 